1. Field of the Invention
The present invention relates to a wind turbine and to a method for assembling and installing a generator for a wind turbine, said wind turbine comprising a nacelle, said nacelle being installed on top of a generally vertical tower, said nacelle comprising a mainframe suitable for installation of a number of components such as, e.g., a generator, a main shaft, and a hub comprising a number of blades, said nacelle further comprising a nacelle cover extending over said main frame from the hub and to a rear end, covering components installed on the main frame.
2. Description of Related Art
It is well known that a modern wind turbine in the Mega Watt class has a nacelle on top of a tower, where various components are arranged. An example of such a component is a generator that via a main shaft is connected to a rotor with a number of wind turbine blades. During installation of the wind turbine, a complete nacelle including all the components that have to be installed in said nacelle can be hoisted to the top of the tower and installed in one piece. As the wind turbines grow larger and larger over time such a nacelle is becoming quite heavy. A complete nacelle for, e.g., a modern 6 Megawatt wind turbine actually weighs more than 230 metric ton. Installing such a component requires use of very large cranes, which only can be operated at wind speeds below a certain value. Further large wind turbines are often installed offshore which also raises extensive and demanding requirements to the equipment used and to the wind speed and also to the size of the waves.
Due to the above mentioned conditions it often becomes expensive to install such wind turbines as it is very common that an installation must be postponed or stopped due to, e.g., wind and/or waves. The crane or cranes will then be on standby and awaiting better conditions. In order to overcome some of the disadvantages by having large cranes hoisting large and heavy components to the top of e.g., a 100 meter high tower, the components can be installed individually by smaller cranes and it might be possible to install some of the minor parts at higher wind speeds than when handling a complete nacelle. This—however—gives another challenge as the nacelle needs to be constructed in a manner that allows it to be opened, so the different components can be installed from above and onto the mainframe in the nacelle. If for any reason one of the components in the nacelle fails and need to be replaced, it is also necessary to get access to the nacelle. Thus, it is very common to have the nacelle cover put together from various parts designed so the nacelle cover can be opened, e.g., with the top of the cover attached to a hinge allowing the top to be swung to the side or simply by lifting and removing at least the top of the nacelle cover. This will give access to the nacelle, but still either of the known solutions is time consuming and expensive and extra work has to be carried out at the nacelle.
Such parts are normally bolted together, but until now the interfaces still allows for some rain water to access the nacelle which is highly unwanted.
One of the larger problems to solve when opening a nacelle cover, either by opening a hinged nacelle cover part or simply by removing a part of the nacelle cover, is to handle the rather large and lightweight items at perhaps 100 meters of height at a location with at least some wind.
Another problem is to design the nacelle cover, especially to design the interface between the respective nacelle cover parts in a manner that will keep rain water from entering the nacelle. This seems to be quite a problem and so far this problem has been addressed, but still no proper solution has been made.